While some changes associated with epididymal maturation are probably preprogrammed during spermatogenesis, interaction of sperm with the epididymal epithelial secretory products are necessary to yield sperm of normal fertilizing capacity. Possible sources of these "secretory" components are: (a) de novo synthesis within epididymal epithelial cells followed by secretion to the lumen; (b) absorption of lumenal fluid components, modification in epithelial cells and secretion back to the lumen; (c) uptake of blood components via the capillary bed, passage through epididymal epithelial cells with or without modification, followed by secretion to the lumen. We have established that glycerolphosphorylcholine (GPC) accumulation in the epididymal lumen is due to the metabolism of blood lipoproteins by epididymal epithelial cells as outlined in mode (c) above and concluded that, while the direct importance of GPC secretion to epididymal maturation is unclear, the process is related to more important types of lipid metabolism. Since lipoprotein metabolism is difficult to impossible to study on a molecular level intact animals, we have established methods for the isolation of principal and basal cells from the rat epididymal epithlium and for the culture of the cells. Preliminary data establish that many lipoprotein lipid components can be metabolized to compounds previously associated with epididymal maturation (GPC accumulation and cholesterol and cholesterol sulfate addition to sperm) or else logically related to epididymal function (prostaglandin biosynthesis and triglycerid metabolism). The proposed experiments will establish which epididymal cell type(s) (principal vs basal) has the capacity to bind and remove lipids (cholesterol, phosphatidylcholine, triglyceride) from the various classes of circulating lipoproteins (chylomicrons, VLDL, LDL, or HDL) and convert these lipids to compounds related to epididymal function (GPC, prostaglandins, cholesterol sulfate, free fatty acids). The final objective is to establish the cells in culture without androgen-supplementation to test for the androgen dependency of these metabolic transformations. Data obtained from these experiments will more precisely define the role of epididymal cells in providing the environment necessary to the epididymal maturation of sperm.